I assume you dont mean you want to buy just one ASIC, which is fine for hobbyist mining but definitely not for profitable mining. Considering your background in altcoin mining using GPUs, this is a tougher nut to crack unless you have a decent factory of ASICs running.

So first decide what you really want to do?

Mine bitcoin for pursuing a hobby and then sell the devices to someone running the same hobby? Or
Mine bitcoin to make money?